Television cameras



J1me 1966 F. RUDERT TELEVISION CAMERAS 2 Sheets-Sheet 1 Filed Dec. 24, 1962 nm w 1 MMMA mw.

M A 0 M w June 7, 1966 F. RUDERT 3,255,309

TELEVI S ION CAMERAS Filed Dec. 24, 1962 2 Sheets-Sheet 2 FIG. 2

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Attorney United States Patent 3,255,309 TELEVISION CAMERAS Frithjof Rudert, Darmstadt-Eberstadt, Germany, assignor to Fernseh G.m.b.I-I., 'Darmstadt, Germany Filed Dec. 24, 1962, Ser. No. 246,799 Claims priority, applileation Germany, Jan. 5, 1962,

5 Claims. 61. 178-7.2)

' being long in relation to the periodicity of field deflection.

The means provided for producing the periodic deflection of the electron image most conveniently consists of coils arranged in the vicinity of the photocathode, the field of which is effective only substantially in the neighborhood of the photocathode and which are traversed by alternating currents of appropriately low frequency.

The most suitable path for the movement of the electron irnage produced by this auxiliary deflection system has proved to be approximately circular, since such a path yields the highest probability that the brightness of all the picture points will be changed and thus yields the most effective protection against burn-in. To produce a circular motion of the electron image it is necessary to produce a rotary field in addition to the uniform axial magnetic field used to image the photocathode upon the target. In the simplest case such a rotary field may be produced by means of two crossed pairs of deflection coils which are traversed by alternating currents of appropriate frequency and differing in phase by 90. It is also'possible to provide a greater number of pairs of deflecting coils, for example three such pairs mutually displaced about the axis by 120, which would be fed from the three phases of a three-phase alternating current supply of very low frequency.

In all television cameras of this type there exists the necessity of producing very low frequency alternating currents having waveforms which are as closely sinusoidal as possible. It has been found by investigation that the most suitable periodicity for the movement of the electron image is between 1 and revolutions per minute; this corresponds to a frequency of 0.0167 to 0.167 c./s. for the alternating currents used to produce the auxiliary defiection.

The production of alternating currents of such extremely low frequencies presents particularly difficult problems.

It has formerly been usual to produce such low-frequency alternating currents by mechanical means, the voltage being taken from a potentiometer, traversed by a direct current, of which the sliding contact is rotated by means of an electric motor. It is certainly true that with such an arrangement it is possible to produce the required current waveform, even at very low frequencies. The arrangement possesses, however, the disadvantage that a considerable amount of mechanical power is necessary to overcome the frictional losses in the potentiometer, which must be provided by an electric motor of In addition, the use of a slider-type The unavoid able fluctuations in the contact resistance of the sliding contact are particularly disadvantageous. Instead of the Patented June 7, 1966 desired slow and uniform movement of the electron image these fluctuations of contact resistance introduce abrupt alterations of position which result in a considerable loss of resolution in the television picture owing to the storage effect of the target.

The principal object of the present invention is to provide novel means for generating two or more alternating currents of very low frequency of different phase for feeding auxiliary deflection means in television cameras.

A further object of the invention is to provide for an arrangement for the purpose set forth which yields more satisfactory results. a

It is afurther object of this invention to provide for an arrangement of the type mentioned which is comparatively simple in its structure and reliable in operation.

Other objects and advantages of the invention will, of course, become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specification in connection with the accompanying drawings in which:

FIGURE 1 shows in schematic perspective an embodiment of a television camera in accordance with the present invention,

FIGURE 2 is a diagram which is used to explain how 'two alternating currents mutually displaced in phase by can be produced by means of a single rotary shutter, and

FIGURE 3 shows waveforms representing the currents produced as described in relation to FIGURE 2.

According to the present invention there is provided a television camera comprising means for subjecting electrons emitted from the photocathode of an image-orthicon camera tube to an auxiliary periodic deflection of which the period is long compared with that of the field deflection in the television scanning process, said auxiliary deflection being produced by means of appropriately disposed coils to which there are applied currents developed by means of a rotary shutter arranged periodically to vary 'the amount of light falling upon electrically light-sensitive devices so disposed in relation to said shutter as to develop currents of like waveform but of different phase. The arrangement according to the invention possesses 'the advantage that the rotary shutter requires only a minimum of driving power, since there are no frictional losses other than the negligible bearing friction. Owing to the omission of sliding elements no appreciable wear takes place and the arrangement therefore operates without disturbance for long periods. By giving the rotary shutter an appropriate form the alternating currents produced may be made of any desired waveform and in particular may be given a very close approximation to a sinusoidal waveform.

In a preferred embodiment of television camera according to the invention there is used to drive the rotary shutter the motor of a working-hours counter, which is in any case commonly provided in television cameras.

'The rotary shutter is then coupled by way of appropriate reduction gearing to a shaft in the working-hours counter which turns at a suitable speed. The additional load is so small that it can be supplied without any alteration to the motor of the working-hours counter. The device then starts automatically upon switching-on the camera,

since the working-hours counter is then arranged to be set into operation. v

FIGURE 1 shows schematically the arrangement of those components of a television camera with which the present invention is concerned. These are contained within :a casing 1, of which the general outline only is indicated.

Within this case is provided a television camera tube 2 of the image-orthicon type, upon the photocathode of which an optical image is projected by means of an objective a lens 3. The image-section of pickup tube 2, in which an electron image of the emission from the photocathode is transferred to the target electrode, is surrounded by a coil system including standard deflection coils for producing the necessary imaging magnetic field and in addition by two pairs of mutually perpendicularly disposed auxiliary deflection coils 4, 4 and 5, 5. The standard deflection coils and the auxiliary deflection coils receive from direct-current amplifiers 6, 7 "respectively alternating currents which are developed in the manner now to be described.

Light from a light source 10, which may conveniently be an incandescent lamp, is directed by means of mirrors 11, 12 towards lenses 13, 14- by which the light is concentrated upon slits 15, 16 in an otherwise opaque diaphragm. Behind the diaphragm there is mounted a shutter 17, conveniently in the form of an eccentrically mounted disc, which alternately obstructs and frees each of the two slots 15, 16. Light which passes through these slots falls respectively upon one of two photocells 8 and 9, thus generating currents proportional to the illumination of the cells which are fed by Way of direct-current amplifiers 6, 7 respectively to the sets of deflection coils 5, 5' and 4, 4 and to the standard deflection coils. Shutter disc 17 is connected by way of a suitable mechanical drive 18 with a shaft of the working-hours counter 19, so that disc 17 is driven by the motor 20 which operates the working-hours counter. The speed of rotation of the shutter 17 is chosen to correspond with the desired period of the raster movement upon the target electrode. The amplitude and waveform of the alternating current produced by the arrangement described is independent of the frequency, so that substantially sinusoidal currents of sufficient amplitude may be produced even at the extraordinarily low frequencies which are necessary.

The two slits 15, 16, which are disposed at the same radial distance from the shutter axis, are mutually displaced about the axis by one-quarter of a revolution. As is further discussed below in relation to FIGURE 2, there may thus be produced with a single rotary shutter two alternating currents which are mutually displaced in phase by 90. It is obviously also possible to produce in an analagous manner, by the use of three slits mutually displaced by 120 in conjunction with three photocells and amplifiers, three-phase currents which may be applied to three pairs of auxiliary deflector coils also mutually displaced by 120 about the image section of the camera tube.

The rotary motion of the charge image produced by the auxiliary deflection coils 4, 4' and 5, 5' is compensated for by causing an auxiliary deflection of the opposite sense in the scanning section of the image orthicon 2, as known in the art.

In FIGURE 2 a number of positions of the edge of the shutter disc 17 are shown in relation to two slits 15, 16 which are mutually displaced about the axis of rotation of the disc by 90. The axis about which the disc rotates is indicated by reference numeral 21 while the path traced by the centre of the disc is indicated by line 22. When the centre of the disc lies at position a the edge of the disc occupies the position indicated by line a, a". In this position the disc leaves the whole length of slot free, so that the light then falling upon the associated photocell 8 is then a maximum. The output current of the cell 8, of which the variation with disc position is indicated by the lines s in FIGURE 3 reaches its maximal value. In this position of the disc, slot 16 is half-covered, so that the current r in the associated photocell 9 possesses only half its maximum ampulitude,'as indicated by the corresponding line r in FIGURE 3.

After a quarter of a revolution of the shutter disc 17 its centre lies at b and its edge lies along the line b'b". It may be seen that slot 15 is now half-covered; the output current of the associated photocell 8 is therefore reduced to one half its maximum value. Slit 16, on the other hand, is now completely free so that the output of the associated photocell is a maximum. After a further quarter-revolution of rotation the centre of the disc lies at c and its edge along cc". Slit 15 is now completely covered so that the output from photocell 8 is a minimum, while slit 16 is now only half-covered, so that the current from photocell 9 now reaches half its maximum value. After yet another quarter-revolution the centre of the disc lies at d and its edge at dd", so that slit 15 is now only half covered and slot 16 is completely covered. It may be seen from FIGURE 3 that the resultant photocell currents, and thus the currents fed from direct-current amplifiers 6, 7 to coil systems 5,5 and 4,4 are substan tially sinusoidal functions of the angular position of the disc and are mutually diaplaced by By giving an appropriate form to the edge of the disc the exact sinusoidal waveform may be approached as closely as is desired.

It is also possible, by an appropriate construction of the amplifier, to arrange that the output current of the amplifier does not vary unidirectionally between a maximum and a minimum value, but that its mean value is zero and that the current rises to alternate maxima in the positive and negative sense. It is thus arranged that the displacement of the electron image on the target electrode is symmetrical with respect to its undeflected position. By shifting the zero line it is possible to compensate for tolerances in the camera tube and in the associated coil assembly, so that the centre-point of the electron image is caused to lie on the optical axis and thus at the centre of the optical image.

What is claimed as new and desired to be secured by Letters Patent is:

1. A television camera comprising means for subjecting electrons emitted from the photocathode of an imageorthicon camera tube to an auxiliary periodic deflection of which the period is long compared 'with that of the field deflection in the television scanning process, said auxiliary deflection being produced by means of appropriately disposed coils to which there are applied currents developed by means of a rotary shutter arranged to vary periodically the amount of light falling upon electrically light-sensitive devices so disposed in relation to said shutter as to develop currents of like waveform but of different phase.

2. A television camera comprising means for subjecting electrons emitted from the photocathode of an imageorthicon camera tube to an auxiliary periodic deflection of which the period is long compared with that of the field deflection in the television scanning process, said auxiliary deflection being produced by means of appropriately disposed coils to which there are applied currents developed by means of a rotary shutter arranged to vary periodically the amount of light falling upon electrically light-sensitive devices so disposed in relation to said shutter as to develop currents of like waveform but of different phase, said rotary shutter is driven through suitable gearing from a shaft rotating at an appropriate speed in a working-hours counter comprised within said tele- VlSlOIl camera.

3. A television camera comprising means for subjecting electrons emitted from the photocathode of an imageorthicon camera tube to an auxiliary periodic deflection of which the period is long compared with that of the field deflection in the television scanning process, said auxiliary deflection being produced by means of appropriately disposed coils to which there are applied currents developed by means of a rotary shutter arranged periodically to vary the amount of light falling upon two electrically light-sensitive devices, each associated with a fixed radial slit in an opaque mask, said slits being relatively displaced about the axis of rotation of said shutter by 90 so that said light-sensitive devices develop alternating currents mutually displaced in phase by 90.

4. A television camera comprising means for subjecting electrons emitted from the photocathode of an imageorthicon camera tube to an auxiliary periodic deflection of which the period is long compared with that of the field deflection in the television scanning process, said auxiliary deflection being produced by means of appropriately disposed coils to which there are applied currents developed by means of a rotary shutter arranged periodically to vary the amount of light vfalling upon two electrically light-sensitive devices each associated with a fixed radial slit in an opaque mask,.said slits being relatively displaced about the axis of rotation of said shutter by 90 so that said light-sensitive devices develop alternating currents mutually displaced in phase by 90, said rotary shutter is so formed that the current generated in each said light-sensitive device is substantially sinusoidal.

5. A television camera comprising means for subjecting electrons emitted from the photocathode of an imageorthicon camera tube to an auxiliary periodic deflection of which the period is long compared with that of the field deflection in the television scanning process, said auxiliary deflection being produced by means of appropriately disposed coils to which there are applied currents developed by means of a rotary shutter arranged periodically to vary the amount of light falling upon two electrically light-sensitive devices each associated with a fixed radial slit in an opaque mask, said slits being relatively displaced about the axis of rotation of said shutter by 90 so that said light-sensitive devices develop alternating currents mutually displaced in phase by 90, light from a source is arranged to be directed upon each of said slits by like optical means, said rotary shutter is so formed that the current generated in each of said lightsensitive devices is substantially sinusoidal, said rotary shutter is driven through suitable gearing from a shaft rotating at an appropriate speed in a workings-hours counter comprised Within said television camera;

References Cited by the Examiner UNITED STATES PATENTS 1,337,737 4/!1920 Van Der Bijl 250-233 2,632,864 3/1953 Hunter 315'l0 X 2,648,782 8/1953 Argabrite 2S0'u2,33 X 2,953,710 9/1960 De Witt 1787.2

DAVID G. REDINBAUGH, Primary Examiner.

JOHN MCHUGH, Assistant Examiner. 

1. A TELEVISION CAMERA COMPRISING MEANS FOR SUBJECTING ELECTRONS EMITTED FROM THE PHOTOCATHODE OF AN IMAGEORTHICON CAMERA TUBE TO AN AUXILIARY PERIODIC DEFLECTION OF WHICH THE PERIOD IS LONG COMPARED WITH THAT OF THE FIELD DEFLECTION IN THE TELEVISION SCANNING PROCESS, SAID AUXILIARY DEFLECTION BEING PRODUCED BY MEABS OF APPROPRIATELY DISPOSED COILS TO WHICH THERE ARE APPLIED CURRENTS DEVELOPED BY MEANS OF A ROTARY SHUTTER ARRANGED TO VARY PERIODICALLY THE AMOUNT OF LIGHT FALLING UPON ELECTRICALLY LIGHT-SENSITIVE DEVICES SO DISPOSED IN RELATION TO SAID SHUTTER AS TO DEVELOP CURRENTS OF LIKE WAVEFORM BUT OF DIFFERENT PHASE. 